Moving from a SR Suntour crank to a Shimano crank...

My bike has a SR Suntour crank with what looks like a PF bottom bracket. There is no visible outboard bearings. I want to swap my cranks for Shimano or Sram. Can I change to a threaded BB or do I have to use a PF BB? Thanks

Yes, it should work fine. You'll probably have to adjust the front derailleur limit screws and front derailleur cable.
Technically you should have the bottom bracket shell faced. External bearings are aligned by the outer edges of the shell.